Such apparatuses are required in road construction machines, for example, and especially in recycling machines for road construction. Such a road construction machine has been described, for example, in WO 96/24725. It comprises a rotation chamber in which a revolving working roller is arranged, which is usually arranged in a height-adjustable and inclination-adjustable manner for adjustment to the surface to be processed. In this rotation chamber, an existing road surface is milled off, the milled material is crushed, bonding agents and especially foamed bitumen are added, and the material is mixed, distributed and supplied to an applying apparatus for forming a new road surface.
An apparatus for producing such a bonding agent and especially foamed bitumen for road construction machines is known from WO 95/22661. The apparatus comprises at least one reaction chamber in which a mixing device is provided in which hot bitumen at a temperature of 180° C. and water can be mixed together via injection nozzles under pressure. The apparatus comprises a heatable foam reactor and heatable feed and distributor lines, wherein the lines can additionally be insulated. Several nozzles are arranged next to one another along a distributor line. This distributor line is connected with a central foam reactor via a line network, in which the foamed bitumen is produced for all nozzles. An agitator is further arranged in this foam reactor. The disadvantage of this apparatus is that the foam reactor is disposed far away from the injection nozzles and the already mixed foamed bitumen will partly disintegrate on its way to the nozzles, so that, among other things, precise dosing of the foam is not possible.
In the production of foamed bitumen or similarly foamed bonding agents, hot bitumen, reaction water and optionally air are preferably injected into a mixing device or a reaction chamber of the road construction machine which is arranged therein and injected from there directly into the rotation chamber. The common injection leads to a mixing of the individual substances in the reaction chamber. During the injection and the contact with the hot bitumen the water will evaporate immediately and will lead to the formation of foamed bitumen and thus to the desired increase in the volume of the bonding agent. The distribution of the water is improved by the addition of air to the hot bitumen and the reaction water, so that the foam quality improves. The finished foamed bitumen can enter the rotation chamber of the road construction machine from the reaction chamber and the mixing device which is arranged therein, where it is then mixed with the raw road material. This finished material mixture is then applied to a substructure as a new road surface by way of respective application and smoothing devices.
The mixing device therefore comprises a reaction chamber, into which at least parts of an inlet device and an outlet device will open, for example, a plurality of separate inlet nozzles for each reaction material to be processed into foamed bitumen. Hence, usually at least one water nozzle, one bitumen nozzle and, in the case of separate introduction of air, also one air nozzle are therefore provided. The outlet device usually comprises a fluidic connection from the reaction chamber to the rotation chamber of the road construction machine, with an injection nozzle also being used in this case by means of which the readily mixed foamed bitumen is sprayed into the rotation chamber.
The entire reaction chamber, including the inlet and outlet devices, is in contact with bitumen during the production of the foamed bitumen. When the device is at a standstill, e.g., during breaks, after ending the work or during maneuvering processes of the machine, the danger therefore is that by cooling and hardening of the bitumen the inlet and outlet devices, and especially the provided injection nozzles, will get clogged and will no longer work upon re-start.
The danger of clogging is also given for the injection nozzle of the finished foamed bitumen or a similar component by means of which the foamed mixture is supplied to the rotation chamber of the road construction machine and comes into contact with the cold milling material.
In the case of low injection quantities, which are usually accompanied by a low injection pressure or partly deactivated nozzles, it can principally occur that the nozzles will be blocked by material from the outside and will be clogged. There are different consequences to this. For example, the finished foamed bitumen is not foamed or not sufficiently foamed by a lack of reaction water or a lack of reaction air, depending on which of the nozzles of the inlet device are clogged. The foam quality is consequently reduced. This has a direct influence on the finished road construction material, the quality of which is influenced negatively. In the region of the outlet device, the clogging of the outlet nozzle, for example can lead to bright strips in the mixing material or regions in which there is no bonding agent at all in the milling material.
Hitherto, the function of the devices can hardly be monitored because of the difficult accessibility to the inlet and outlet devices and especially to any nozzles within the rotation chamber or within the reaction chambers.
An apparatus is known from the prior art which intends to remedy this problem. DE 102 41 067 B3 describes an apparatus for producing foamed bitumen which comprises a stripping device on the respective inlet nozzles by means of which clogged nozzles can be “scraped free”.
DE 297 02 162 U1 describes an apparatus for producing foamed bitumen, in which a pressure journal is provided for each nozzle for cleaning potentially clogged nozzles, which journal is able to punch through any possibly clogged nozzle. The disadvantageous aspect is that complex routing of lines is necessary in order to provide space for the cleaning cylinder. For this purpose, the foamed bitumen needs to be redirected at first to a kind of a secondary chamber before then exiting into the rotation chamber of the road construction machine. The foam may lose some of its quality already by this redirection.
The initially described apparatuses therefore come with the disadvantage that the cleaning apparatuses for the inlet and outlet devices, especially for clogged nozzles, require a very complex construction, with a preceding test for perfect functioning of the inlet and outlet devices not being possible at all. Malfunctions and lack of quality of the finished product are the consequence.